Hey you get a gold star from me for your first post! You make an extremely valid point(s). I just discussed with my wife your post also. I think if we had her dad build us a nice foundation it would improve anything we bought. As it is we have a rail frame for the mattress which leaves little but the outside edges truly supported which is where the sag comes into play. Her dad is an outstanding carpenter...the furniture in our house a small but high quality snippet of his wood working experience. Like you say we can buy the best "normal" mattress for our money and add a slab of memory foam later when we have the money...if we think we need it.
This would be a very helpful route as the guy I know will give me an extra $100 off for computer work I've done for him plus he owes me $250 yet... I've just got to be able to get a hold of him at home!
So my next question then is are there others who have used just the memory foam pad and liked it just as well?